When administering a medicament by means of a medicament delivery device, it may for certain applications be of importance to register the time of administration and the size of the dose.
Traditionally, such logs were kept manually by the user. This however required that the user was able to remember to write down the correct information at every occasion of medicament administration. The disadvantages of this method have resulted in a drive towards the development of medicament delivery devices that can handle logging automatically.
An example of such automatic logging is disclosed in EP1804868. This document discloses a medication delivery device that comprises an injection device having a reservoir comprising a medicament to be ejected, and a sensor arranged to detect an ejection of the medicament from the injection device, and a processor. The sensor is arranged to output a signal comprising ejecting information. The processor collects and stores the ejection information.
The medicament delivery device disclosed in EP1804868 is of the type which has a piston rod that is displaced linearly inside the housing without rotation relative to the housing.
There are however medicament delivery devices on the market that have piston rods provided with a threaded outer surface, where linear displacement of the plunger rod is achieved by means of rotation thereof. For these types of medicament delivery devices there are currently no solutions for automatic logging where it can be made certain that detection of displacement of internal parts can be attributed to medicament administration.